As electronic component mounting densities have increased, mounting techniques known as “chip scale package” and “chip size package” in which the dimensions of the semiconductor mounting substrate are about the same as the semiconductor chip dimensions, have attracted interest. For example, as shown in FIG. 1, a semiconductor chip 1 is bonded by adhesive 3 to a mounting substrate 2 having the same dimensions, solder balls (interconnect pads) 4 are formed on the back face of mounting substrate 2, and the semiconductor chip 1 and solder balls 4 are interconnected by wire bonding 5 using an opening made in the center of the mounting substrate 2, for example. As shown in FIG. 2, the wire bonding 5 is sometimes formed using the outside of the semiconductor chip 1. In FIG. 2, there is a copper foil pattern 6 on the surface of substrate 2, interconnecting the wire bonding 5 and solder balls 4. Or, as shown in FIG. 3, an opening in the interior of the semiconductor chip 1 can be used for formation. In this case an extension 7 of the copper foil pattern is used for interconnection of the semiconductor chip 1 and solder balls 4.
Bonding of the semiconductor chip and mounting substrate in this kind of semiconductor chip package can be accomplished with liquid adhesive, but adhesive sheets are used due to ease of control in fabrication processes. The adhesive sheet may be an adhesive of sheet form, but typically one having adhesive layers formed on both sides of a heat resistant base material or core material is used. Heat resistant base materials and core materials used include polyimide resin, polycarbonate, polyester, polytetrafluoroethylene, polyethylene, polypropylene etc.; in addition to solid sheets, the use of porous sheets is also known. Epoxy resin is a typical adhesives although maleimide, cyanate or other resins are also used (Unexamined Patent Application 10-340968, Unexamined Patent Application 2000-154356, Unexamined Patent Application 10-22325 etc.).
Adhesives for use in conventional IC chip bonding sheets consist exclusively of materials containing bromine to impart flame retardance. However, in recent years improvements in global consciousness with regard to environmental problems has led to strong demand from the market for products that do not contain bromine or other substances that can emit toxic gases when burning.
Accordingly it is an object of the present invention to provide an IC chip bonding sheet that while employing bromine-free adhesive resin nevertheless offers high flame retardance, as well as reliable performance in terms of heat resistance, humidity resistance, resistance to thermal expansion etc., and an IC package employing same.